The structure, function and utilization of eukaryotic promoter sequences required for the specific intiiation of RNA transcription are being studied, The endogenous retrovirus CPC-1 isolated from Colobus polykomos kidney cells provides a unique probe to dissect the modulators of eukaryotic gene expression. Specific goals are (1) to elucidate the specific DNA signal sequences (promoters) which control efficient transcription; (2) to ascertain the nature of the factors which modulate recognition of transcriptionally active genes; (3) to develope efficient eukaryotic cloning vectors.